There have already been numerous reports of siliconemodified phenolic resins and methods for their preparation. For example, Japanese Patent Application Laid Open [Kokai] Number 50-129699 [129,699/75] discloses a method in which phenolic resin and straight-chain organopolysiloxane having the alkoxy group at both molecular chain terminals are condensation reacted by heating. Otherwise, Japanese Patent Application Laid Open Number 61-192711 [192,711/86] discloses a method in which phenolic resin is condensation reacted by heating with organopolysiloxane resin having the alkoxy group or hydroxyl group at the molecular chain terminals.
However, these prior methods suffer from production problems. For example, due to the use of organopolysiloxane which in all cases is incompatible with the starting phenolic resin, the condensation reaction rate is slow, and long periods of time are thus required to obtain the silicone-modified phenolic resin. Moreover, the silicone-modified phenolic resins afforded by these methods have an unsatisfactory heat resistance because they inevitably contain the straight-chain diorganopolysiloxane unit, and this restricts their application.